Polishing systems are used to remove material from a wafer. A polishing system includes a carrier head which presses the wafer against a polishing pad. The polishing pad or the carrier head rotate relative to each other which results in material being removed from the wafer. In some instances, a slurry compound is applied to the polishing pad to assist in material removal.
The carrier head includes a retainer ring which is positioned to help prevent the wafer from moving during the polishing process. The retainer ring is also pressed against the polish pad during the polishing operation. As the carrier head or polishing pad rotate, a portion of the polishing pad which is contacted by the retainer ring is also used to remove material from the wafer.